ORR activity and stability of Pt-based and Pt-free catalysts for PEMFC applications

Abstract

Aiming at the development of stable and highly ORR active catalysts for PEMFC applications, different Pt-based and Pt-free catalyst materials were developed and characterized regarding their physical and electrochemical properties. For the Pt-based catalysts, composite materials containing electrically well-conducting carbon nanotubes and highly oxidation-stable titania were used as support materials for Pt nanoparticles in order to increase their stability while maintaining the catalytic activity of carbon-supported Pt nanoparticles. The Pt-free catalysts consist of a nitrided and amorphous carbon core and an oxidation-stable metal (oxy)nitride shell (titanium (oxy)nitride, tantalum (oxy)nitride), with both parts acting as ORR catalyst. Additionally, the ORR-active, nitrided carbon cores were characterized, as well. Experimental results and simulations of model catalysts were combined in order to gain information on the ORR reaction pathways on nitrided carbon catalysts as well as the correlation between the structure, e.g., porosity and N-content, and the ORR activity.